This invention relates to drip irrigation and, more particularly, to a drip irrigation hose with an improved outlet construction and a method for its manufacture.
Drip irrigation hose can be classified into two types--hose having discrete emitters and hose having continuous, integral emitters. An example of a drip irrigation hose having discrete emitters is shown in U.S. Pat. No. 4,850,531. An example of a drip irrigation hose continuous, integral emitters is shown in U.S. Pat. No. 4,247,051. Drip irrigation hose having continuous integral emitters offers the possibility of lower cost and ease of manufacture and installation.
The design of the inlets to and outlets from the emitters is critical. If the effective outlet area of the emitters is too large, dirt and debris can collect externally in the outlets, thereby causing external clogging. If the effective inlet and outlet areas of the emitters are too small, they become clogged internally and cease to serve their purpose. Further, if the effective outlet areas of the emitters are too small, water squirts out of the hose instead of dripping, and soil erosion results.
U.S. Pat. No. 4,247,051 discloses a drip irrigation hose formed by bending a strip plastic film along its length to form an overlapping longitudinal seam between opposing longitudinal margins of the film. First and second longitudinally extending, laterally spaced, transverse ribs interconnect the opposing margins along their length to seal the overlapping longitudinal seam. The ribs are formed by one or more molten plastic beads extruded onto the film. As a result, a flow regulating passage is defined by the ribs and the opposing margins and a supply passage is defined by the remainder of the film. Water flows from the supply passage to the flow regulating passage through a plurality of longitudinally spaced inlets. Water flows from the flow regulating passage to the exterior of the hose through a plurality of longitudinally spaced outlets longitudinally spaced from the respective inlets to provide a substantial path length from each inlet to a respective outlet. In one embodiment, the outlets each comprise two parallel knife blade formed slits that create between them a flexible flap. The flap serves as an outlet valve, opening and closing as the hose is pressurized and depressurized. However, unless the plastic film is very thick and rigid, the flaps do not close consistently when the hose is depressurized and therefore, the outlets can become clogged by soil drawn into the slits.
In other types of drip irrigation hose, elongated slot-like outlets are sometimes formed by a laser than vaporizes part of the plastic film. When the water is turned off, the outlets may not completely close because of the removed material.
A problem encountered in the manufacture of continuous emitter drip irrigation hose is coordinating the position of the outlets and the track pattern of the ribs. If care is not taken, the track pattern of the ribs may overlap the outlets, and thereby cause the outlets to be on the high pressure side of the flow regulating passages.